This invention relates to a motor frame with increased cooling capacity and a motor constructed with such a frame. As is well known in the art, one of the factors limiting the operation of a motor is the ability of the physical structure of the motor and its enclosure to dissipate heat. Motors are rated based on their ability to operate in a continuous steady state at a given temperature below a maximum allowable temperature. These limitations are imposed not only to prevent premature wear and failure of the motor, but to prevent unsafe conditions resulting from extremely hot motor parts which could ignite adjacent materials.
Various techniques for dissipating heat are known, and include providing fins on the exterior of the motor frame. Heat dissipation is enhanced by the fins as a result of a greatly increased surface area in contact with the environment. Heat travels from the stator through the thickness of the frame at a given rate by conduction and radiates into the atmosphere from the surface of the exterior of the motor frame by convection and radiation. The fins permit the heat transfer rate to be increased.
The preferred embodiment of the invention disclosed below is shown on a brushless direct current motor which operates on alternating current. In the prior art version of this type of motor, a wound stator extends around the inside of the motor frame in intimate contact with the smooth, continuous, inner walls of the frame. A rotor onto which magnets are secured rotates within the void of the stator. Heat generated in the stator during operation of the motor is conducted through the solid walls of the motor frame and into the vicinity of the fins, where the heat radiates into the air by convection and radiation. The invention described below permits heat to be dissipated from the motor at a much greater rate, thereby permitting the motor to operate under more severe load and environmental conditions without detrimental effects.
The invention also permits the use of a single, extruded aluminum extrusion to build totally enclosed or open, externally ventilated motors. Motors that are totally enclosed, non-ventilated depend entirely on the removal of heat from the frame surface by natural convection and radiation. Motors that are totally enclosed, fan cooled or totally enclosed air-over rely heavily on the moving of forced air over the motor's exterior fins for improved heat dissipation. Motors having an open construction depend mainly on the moving of cool, outside, ambient air into the interior of the motor and over the hot stator windings, laminations, and then discharge the heated air out of the ventilation openings. The invention according to this application permits motors of both closed and open construction to be built using the same extrusion, and, in addition, provides enhanced cooling.